Fail fast if ENV["STACK"] is missing
Fail fast if ENV["STACK"] is missing

packetmonkey/heroku-buildpack-ruby,fcruxen/ruby-buildpack,ericroberts/heroku-buildpack-ruby,jonasoberschweiber/heroku-buildpack-ruby,donnykurnia/heroku-buildpack-ruby,sky-uk/ruby-buildpack,space150/heroku-buildpack-ruby,Scalingo/ruby-buildpack,cmaggard/heroku-buildpack-turbo-sprockets,cloudfoundry/ruby-buildpack,iamjarvo/ruby-buildpack,swipesense/heroku-buildpack-ruby,ilpoldo/heroku-buildpack-ruby,schu/buildpack-testing,cordata/heroku-buildpack-ruby,recursecenter/heroku-buildpack-ruby,donnykurnia/heroku-buildpack-ruby,dlorson/gentle-buildpack,barakav/heroku-buildpack-ruby,cordata/heroku-buildpack-ruby,brightbytes/heroku-buildpack-ruby-without-assets-precompile,dleavitt/heroku-buildpack-ruby,beydogan/ruby-buildpack,ekaranto/rails4-bluemix-buildpack,hpcloud/ruby-buildpack,Altoros/ruby-buildpack,jumptvs/BP_Ruby,orenyk/heroku-buildpack-ruby,ericboehs/heroku-buildpack-ruby,mintybit/heroku-buildpack-ruby,HYPERHYPER/heroku-buildpack-ruby,ekaranto/rails4-bluemix-buildpack,icelab/heroku-buildpack-ruby,takii/heroku-buildpack-ruby,markaschneider/heroku-buildpack-ruby-ffmpeg-sox,cloudControl/buildpack-ruby,zoomer/heroku-buildpack-ruby-bower,mperejda/heroku-buildpack-ruby,moneyadviceservice/heroku-buildpack-ruby-bowndler,erintherad/heroku-buildpack-ruby,jonasoberschweiber/heroku-buildpack-ruby,musicglue/heroku-buildpack-ruby,bellycard/heroku-buildpack-ruby,bskyb-commerce/ruby-buildpack,daltonrenaldo/heroku-buildpack-ruby,Micka33/heroku-buildpack-ruby-liblua,pilotcreative/heroku-buildpack-ruby,derrek/heroku-buildpack-ruby,jumptvs/BP_Ruby,electricobjects/heroku-buildpack-ruby,bskyb-commerce/ruby-buildpack,DouglasAllen/heroku-buildpack-ruby,guidance-guarantee-programme/heroku-buildpack-princexml-old,shuber/heroku-buildpack-ruby,pkgr/heroku-buildpack-ruby,zunda/heroku-buildpack-ruby,hpcloud/ruby-buildpack,bwaite-jaroop/heroku-buildpack-ruby,fgbreel/heroku-buildpack-ruby,bskyb-commerce/help-heroku-buildpack,0x00evil/heroku-buildpack-ruby,mattmanning/heroku-buildpack-ruby-jekyll,Jonty/ruby-buildpack,stefansundin/heroku-buildpack-ruby,cloudControl/buildpack-ruby,dlorson/gentle-buildpack,zidekmat/buildpack-ruby,qnyp/heroku-buildpack-ruby-bower,cloudfoundry/ruby-buildpack,codykrieger/heroku-buildpack-jekyll,engineyard/heroku-buildpack-ruby,pietrop/heroku-buildpack-ruby,gbenedict/heroku-buildpack-ruby,leonardykris/mos-ruby-buildpack,cmaggard/heroku-buildpack-turbo-sprockets,hpcloud/ruby-buildpack,rowanoulton/heroku-buildpack-ruby,tpope/heroku-buildpack-ruby-tpope,jonseaberg/heroku-buildpack-turbo-sprockets,vhx/heroku-buildpack,Jonty/ruby-buildpack,hpcloud/ruby-buildpack,DyegoCosta/heroku-buildpack-ruby,ChefSteps/heroku-buildpack-ruby,tdenovan/heroku-buildpack-ruby,cloudfoundry/ruby-buildpack,michaelphines/alexa-nest,jayshreeanand/heroku-buildpack-ruby,ilpoldo/heroku-buildpack-ruby,makifund/heroku-buildpack-ruby,wakermahmud/heroku-buildpack-jekyll,HYPERHYPER/heroku-buildpack-ruby,sky-uk/ruby-buildpack,ericroberts/heroku-buildpack-ruby,Altoros/ruby-buildpack,packetmonkey/heroku-buildpack-ruby,andycroll/heroku-buildpack-jekyll,ekaranto/rails4-bluemix-buildpack,derrek/heroku-buildpack-ruby,beydogan/ruby-buildpack,bskyb-commerce/help-heroku-buildpack,bwaite-jaroop/heroku-buildpack-ruby,reesio/heroku-buildpack-ruby,lyoshenka/heroku-buildpack-ruby-jekyll,andycroll/heroku-buildpack-jekyll,bellycard/heroku-buildpack-ruby,jgable/buildpack-ruby-rack-setup-tasks,ltrademark/heroku-buildpack-ruby,lyoshenka/heroku-buildpack-ruby-jekyll,jumptvs/BP_Ruby,michaelphines/alexa-nest,cloudfoundry/ruby-buildpack,gls1/heroku-buildpack-ruby-pdftk-new,markaschneider/heroku-buildpack-ruby-ffmpeg-sox,heroku/heroku-buildpack-ruby,engineyard/heroku-buildpack-ruby,aarongray/heroku-buildpack-ruby,orlando/heroku-buildpack-ruby,Genius/heroku-buildpack-ruby,swipesense/heroku-buildpack-ruby,schu/heroku-buildpack-ruby,stefansundin/heroku-buildpack-ruby,orenyk/heroku-buildpack-ruby,tdenovan/heroku-buildpack-ruby,daltonrenaldo/heroku-buildpack-ruby,aarongray/heroku-buildpack-ruby,mattmanning/heroku-buildpack-ruby-jekyll,electricobjects/heroku-buildpack-ruby,leonardykris/mos-ruby-buildpack,mperejda/heroku-buildpack-ruby,wakermahmud/heroku-buildpack-jekyll,zidekmat/buildpack-ruby,zunda/heroku-buildpack-ruby,pietrop/heroku-buildpack-ruby,cloudfoundry/ruby-buildpack,amaltson/heroku-buildpack-ruby,codykrieger/heroku-buildpack-jekyll,Dim25/heroku-buildpack-ruby-GSL,DouglasAllen/heroku-buildpack-ruby,DyegoCosta/heroku-buildpack-ruby,erintherad/heroku-buildpack-ruby,vhx/heroku-buildpack,musicglue/heroku-buildpack-ruby,iamjarvo/ruby-buildpack,Jonty/ruby-buildpack,instacart/heroku-buildpack-ruby,space150/heroku-buildpack-ruby,pkgr/heroku-buildpack-ruby,Altoros/ruby-buildpack,dleavitt/heroku-buildpack-ruby,sky-uk/help-heroku-buildpack,bskyb-commerce/ruby-buildpack,fcruxen/ruby-buildpack,makifund/heroku-buildpack-ruby,takii/heroku-buildpack-ruby,iamjarvo/ruby-buildpack,dieze/heroku-buildpack-ruby-hooks,guidance-guarantee-programme/heroku-buildpack-princexml-old,brightbytes/heroku-buildpack-ruby-without-assets-precompile,Jonty/ruby-buildpack,barakav/heroku-buildpack-ruby,ekaranto/rails4-bluemix-buildpack,sky-uk/ruby-buildpack,ChefSteps/heroku-buildpack-ruby,Altoros/ruby-buildpack,pilotcreative/heroku-buildpack-ruby,instacart/heroku-buildpack-ruby,ruby/heroku-buildpack-www-ruby-lang,Scalingo/ruby-buildpack,qstream/heroku-buildpack-ruby,sky-uk/ruby-buildpack,sky-uk/help-heroku-buildpack,orlando/heroku-buildpack-ruby,qnyp/heroku-buildpack-ruby-bower,ericboehs/heroku-buildpack-ruby,bskyb-commerce/ruby-buildpack,iamjarvo/ruby-buildpack,reesio/heroku-buildpack-ruby,gbenedict/heroku-buildpack-ruby,moneyadviceservice/heroku-buildpack-ruby-bowndler,Genius/heroku-buildpack-ruby,jayshreeanand/heroku-buildpack-ruby,fcruxen/ruby-buildpack,ltrademark/heroku-buildpack-ruby,icelab/heroku-buildpack-ruby,dieze/heroku-buildpack-ruby-hooks,fcruxen/ruby-buildpack,fgbreel/heroku-buildpack-ruby,gls1/heroku-buildpack-ruby-pdftk-new,shuber/heroku-buildpack-ruby,heroku/heroku-buildpack-ruby,0x00evil/heroku-buildpack-ruby,zoomer/heroku-buildpack-ruby-bower,jgable/buildpack-ruby-rack-setup-tasks,recursecenter/heroku-buildpack-ruby,qstream/heroku-buildpack-ruby,tenjikinc/heroku-buildpack-ruby,mintybit/heroku-buildpack-ruby,tpope/heroku-buildpack-ruby-tpope,catalyzeio/buildpack-ruby,amaltson/heroku-buildpack-ruby,jonseaberg/heroku-buildpack-turbo-sprockets,Dim25/heroku-buildpack-ruby-GSL,rowanoulton/heroku-buildpack-ruby,tenjikinc/heroku-buildpack-ruby,catalyzeio/buildpack-ruby,schu/heroku-buildpack-ruby,schu/buildpack-testing,jumptvs/BP_Ruby,Micka33/heroku-buildpack-ruby-liblua